The invention concerns simultaneously physical effects, materials, and fabrication processing to significantly increase the efficiency of the light-to-electricity conversion.
The one photon-one electron principle no longer applies when there is generation of additional electrons in a process involving a shallow extrinsic energy level and the conduction band. Here we show that a complementary converter will cool hot electrons (generated by energetic photons) via a specific silicon metamaterial membrane system buried within the emitter at the c-Si/a-Si interface.
From the photoconversion viewpoint there are three modes of photon interaction with matter: transmission, conversion into electron flux (when the photon energy is close to the band gap) and conversion into both electron and phonon fluxes (when the photon energy is clearly above the band gap). Energetic photons produce two fluxes: electron flux→collectable current and phonon flux→energy lost heat. For photon energies that results in carrier multiplication, where the multiplication cycle is characterized by the ratio of additional photon energy to specific segton energy Eδ (the mean value of Eδ is 0.274 eV). A multistage process allows conversion of energetic photons into a electron population. The unused kinetic energy of photogenerated hot carriers, reaching a buried substructure(s) with a nanoscale Si-layered system, is transferred to near-equilibrium electrons collectable in the external circuit.
The multistage conversion cycle starts with the primary generation (photon absorption), then continues with secondary generations by multiple collisions of hot electrons with segtons (due to the specific low-energy mechanism). To ensure the permanent electric charge state of the segton a specific electron transport mechanism within seg-matter through its boarding nanomembranes (interfaces) is absolutely necessary. This charge replenishment depends on the extremely short time constants of the segton dynamics (recharging).
The multiplication cycle depends on the dynamics of the involved carrier population that has to be taken into account situating of the sag-matter within the converter, preferentially within the emitter. So one of the manageable ways is a superposition of desired effects within a limited and suitably localized volume, subvolumes, part(s) of the emitter to assume optimal conditions for the full and efficient cycle of the giant photoconversion.
The modulation of the local material uses simultaneously several physical interactions, such as variation of the matter structure, heavy impurity doping, transition zones of semiconductor interfaces, local stress fields, local electric fields, local electron transport, effective electric screening and well-defined functionality of usefully arranged active components. The conceived material modulation preserves conventional-like behavior of the converter due to, for example, adapted ratios of geometrical factors, useful defect screening, unperturbed free-electron extraction as well as specific electron transport mechanisms.
Using the quantum dots analogy, one can say that the silicon bandgap is controlled by confinement of carriers in artificial semiconductor nanoobjects, i.e., segtons, which behave like individual atoms or molecules. If they are close enough to allow large collision probability, atomic-like electron energy levels appears in the band model of a bulk semiconductor. This gives rise to a new version of the semiconductor material with electrical and optical properties that are tuned by adjusting the seg-matter size, segton density and seg-matter disposition within the converter. A membrane separates carriers of the same electric charge (electrons) but of different kinetic energy, i.e., hot electrons from near equilibrium electrons. Active substructure(s) is(are) embedded within a part(s) of the emitter that distinguishes by its higher doping density from its(their) neighborhood.
This innovation presents a practical realization of the theoretically evoked prediction for the bright future of the highly efficient light-to-electricity conversion due to “semiconductor nanocrystals embedded in semiconductor matrix”. Nanostructured transformations of semiconductors, preferentially of Si, lead to optimized nanocrystal-like nanoobjects, called segtons and corresponding metamaterial, called seg-matter. This is an answer how to operate in practice.
A part of the enhanced functionality is assumed by active nanomembranes that separate appropriately inserted sub-grains from their surroundings. Such subsystems occupy a relatively small part of the converter volume, being grouped essentially in the emitter, rather in a part of the emitter. In this way nanomembranes allow avoidance of undesirable effects resulting from the insertion of a foreign body of active grains. In other words, the inserted subsystems are practically invisible by the host system except for an unperturbed addition of the metamaterial performances to the performance of the conventional components of the converter.
Due to original solutions that has been never used before and that relies on sparsely grafted grains, the designer has much liberty in the converter design and its optimization.
The built-in nanomembrane system or subsystems allow a transformation of a conventional semiconductor bulk, in particular and preferentially silicon, by addition of nanostructured components. Grain-like inclusions bring locally physical conditions necessary to modulate deeply enough the host matter with respect to number, shape, position, size and depth of required generation centers and the corresponding electron transport around them.
Modular architecture allows an optimal arrangement of the converter components interacting with hot electrons by an adjusted distribution of the seg-matter. The efficiency enhancement of the light-to-electricity conversion incorporates also an excellent collection of all electrons (primary and secondary) generated within the converter.